1. Field of the Invention
This invention relates to a reactive power control apparatus for an AC power system, in which a reactive power compensation device, and a compensation capacitor device including at least one compensation capacitor are connected to the system bus of the AC power system, so as to control reactive power in accordance with the voltage fluctuation of the system bus.
2. Description of the Related Art
Patent Document 1 (JP-A-62-269213, particularly FIG. 1) discloses a reactive power control apparatus which employs a reactive power compensation device and a compensation capacitor device in combination. The reactive power compensation device and the compensation capacitor device are connected to the identical system bus of an AC power system. The reactive power compensation device includes a capacitor, a reactor and a semiconductor switch, and it controls the semiconductor switch in accordance with the reactive power of the system bus, so as to compensate the reactive power of the system bus. The compensation capacitor device includes a plurality of compensation capacitors. The individual compensation capacitors are respectively connected to the system bus through switch devices, and they are closed to or opened from the system bus by turning ON/OFF the corresponding switch devices.
The reactive power control apparatus disclosed in Patent Document 1 performs the control of compensating the reactive power which a load consumes during a load fluctuation, by the reactive power compensation device and the compensation capacitor device which are connected to the system bus in parallel with the fluctuating load. The control, however, does not cope with a transient mode at a recovery stage from the abnormal state of the power system. The reactive power compensation device is configured so as to control the reactive power in a wider range than the capacitances of the respective compensation capacitors in the compensation capacitor device. In a case where the abnormal state has occurred in the power system, the reactive power compensation device outputs much reactive power instantaneously, and the respective compensation capacitors of the compensation capacitor device are thereafter closed to the system bus in succession. When the power system has recovered from the abnormal state, a control proceeds so that the reactive power compensation device may absorb surplus reactive power instantaneously, and that the respective compensation capacitors having been closed may be thereafter opened from the system bus. Therefore, the reactive power control apparatus has the problem that the capacity of the reactive power compensation device becomes large.